Palaeomagnetic study of Tertiary volcanic domains in Southern Turkey and Neogene anticlockwise rotation of the Arabian Plate

Abstract

Following collision with Eurasia, the Arabian Shield indenter has continued to deform into the weak Anatolian collisional collage that resulted from subduction of the Neotethyam Ocean. Differential movements have involved rotation and continuing northwards translation, and have been accommodated mainly by slip along major transforms including the northward extension of the Dead Sea Fault Zone (DSFZ) and the East Anatolian Fault Zone (EAFZ). To aid in evaluating post-collisional motions the palaeomagnetism of extensive volcanic domains at the northern margin of the stable shield in southern Turkey is reported here together with the timing of emplacement as constrained by K-Ar study. The age dating results indicate that volcanic activity occurred mainly during mid-late Miocene times corresponding to the final stages of suturing. Volcanic fields in the east of the investigated region are younger and correspond to Neotectonic volcanism in Brunhes and Matuyama chrons. Thermal and alternating field demagnetization of 399 cores from 83 sites in basaltic lavas identifies 29 units of normal and 43 of reversed polarity with 11 sites having transitional or random directions. Volcanic fields west of the Euphrates (Kilis-Gaziantep region) with ages in the range 7.0-20.3 Ma (average 14.9 Ma, SD=4.3 Ma) have mean remanence D/I=353/52 degrees (38 sites, 5.3 degrees). Lava fields east of the Euphrates (Urfa region) are dated 10.4-12.1 Ma and yield a comparable mean remanence D/I=350/50 degrees (17 sites, 6.0 degrees). These collections are shown to have properly recorded palaeosecular variation with only minimal inclination shallowing and inferred anticlockwise rotations with respect to Eurasia since mid-Miocene times are 10.9 +/- 4.3 degrees and 14.0 +/- 5.0 degrees respectively. These contrast with clockwise rotation of 6.3 +/- 4.3 degrees derived from late Matuyama-Brunhes epoch volcanic rocks immediately to the north west of the Arabian margin where rotational impingement of the shield indenter into fault blocks within the Karasu Rift at the northern extension of the DSFZ interacts with left lateral motion at a rate of similar to 0.5 cm/year along this zone to produce small scale vertical axis rotations. Results from the volcanic suites sited on the stable shield are compared with other results from the Arabian Plate to conclude that it did not rotate significantly following closure of the Bitlis Suture until Late Miocene-Early Pliocene times since when it has rotated anticlockwise at a rate of similar to 1.0 degrees/Myr. This is comparable to the present day rate of rotation deduced from GPS and correlates with crustal separation and sea floor spreading in the Red Sea. It also temporally links the rotation of the Arabian Plate to the initiation of the intracontinental transforms (North and East Anatolian fault zones) within Anatolia and to the subsequent extrusion of blocks within this accretionary domain by tectonic escape to the west. (C) 2008 Elsevier B.V. All rights reserved.